1. Field of the Invention
The present invention relates to an user Identification module (UIM) of a mobile communication terminal, and in particular to a method for preventing unauthorized use of an UIM.
2. Description of the Related Art
In general, an UIM (User Identification Module also known as a “SIM card”) is an IC (Integrated Chip) card module inserted into a terminal, and it is commonly used for a global system for mobile communication (GSM) terminal in Europe. An UIM technique applies a security function as a major advantage of an IC card to a CDMA terminal and provides movability, storability, and authentication algorithm as characteristics of the IC card.
In more detail, the UIM is an IC card that can be attached to a terminal and consists of a microprocessor and a memory chip. The memory chip stores personal information of an UIM owner and various information (telephone number and network number) for operating the terminal, and the user (owner) can attach the UIM to another terminal supporting a SIM interface and use the UIM. In addition, when the terminal is turned on, the UIM checks enable/disable attribute of a card holder verification (CHV), when the CHV is enable, it performs user authentication operation by receiving a CHV code from the user.
Hereinafter, the user authentication operation of the terminal attached to the UIM will be described in detail.
After opening a window for changing the CHV enable/disable attribute on a user menu, the user inputs information and a CHV code for changing the CHV enable/disable attribute. When the user inputs information and the CHV code for changing the CHV enable/disable attribute, the terminal transmits the pertinent CHV code to the UIM through a command packet and requires the UIM to change the CHV enable/disable attribute.
The microprocessor of the UIM receives the CHV code as a certain kind of password and performs user authentication operation for judging whether the pertinent user is a network-registered user. When the user is validated, the microprocessor of the UIM changes the enable/disable attribute of the CHV and notifies the user of the change.
Referring to FIG. 1, when the terminal having the UIM is turned on (block S10), the terminal determines a communication protocol (block S11) and a transmission speed through negotiation with the UIM and updates operation parameters (block S12) according to the determined protocol and transmission speed.
The microprocessor of the UIM checks whether the CHV is in the enable state by reading the enable/disable attribute of the CHV (blocks S13 and S14). When the CHV is in the enable state, it receives the CHV code from the user and performs the user authentication (blocks S15 and S16). When the CHV is in the disable state, the microprocessor does not perform the user authentication operation.
As described above, when the CHV is in the enable state, whenever the terminal is turned on, the UIM receives the CHV code from the user and performs the user authentication operation repeatedly. When the CHV is in the enable state, the user has to input the CHV code for the user authentication whenever the terminal is turned on. This can be inconvenient to the user.
Accordingly, in order to bypass the above-mentioned inconvenience, the user sets the CHV of the UIM at the disable state, and accordingly the user can use the UIM freely on the user's own terminal or other people's terminals without passing the user authentication.
However, when the user loses the UIM and the CHV is in the disable state, other people may illegally use the pertinent UIM on another terminal without passing the user authentication. In addition, personal information of the user stored in the UIM may be erased.